I am planing a Surly Trucker Disc Travel-Bike build and now I am stuck on the bottom bracket bearing. The bearing shell is 73mm wide. Is it possible to install a Sram DUB Innenlager BSA 68/73mm? I am not sure since Sram DUB is declared everywhere as MTB, can I use it and what is the difference between a MTB and a 'normal' bottom bracket bearing?
For threaded 'English' or 'BSA' bottom bracket shells, the standard was 68mm wide for road bikes, 73mm wide for MTB. However, some bikes that are not MTBs use the 73mm wide shell and there are now 100mm wide shells for MTBs as well.
By the way, I looked at the Surly Trucker page you linked to, it says the bike has a 68mm shell not 73mm.
In any case, yes you can fit that bottom bracket. It has a version specifically for 68 and 73mm threaded shells. On a 68mm shell, two 2.5mm spacers are used so the width of the installed bracket remains the same.
You will need compatible MTB style cranks with the correct length spindle of course. Many folks get tripped up trying to install road cranks with a shorter spindle for 68mm shells into a putative 'road' bike with a 73mm shell.